A "sexist" demand from Tories to educate her children locally was one of the factors that led Caroline Spelman, the Conservative chairman, to pay a former nanny through parliamentary allowances, it has been claimed.

Spelman will today refer herself to parliament's standards watchdog after admitting that she paid her nanny, Tina Haynes, from her parliamentary staffing allowances for secretarial work.

The Tory chairman confirmed she did this for a few months after she was first elected to the Commons in 1997 because Haynes performed secretarial duties in her Meriden constituency, in the West Midlands, during school hours before looking after her three children later in the day. "At the time, I thought it was entirely within the rules - and that is still my belief," Spelman said.

Friends of Spelman say the unusual arrangements, which will be investigated by the parliamentary standards commissioner, John Lyon, were caused in part by what they describe as the "sexist" demand when she was selected as the Tory candidate in Meriden. Spelman was asked to give an undertaking that she would live in Meriden and educate her children there.

One friend said: "All aspiring MPs are asked if they will live in the constituency. Everyone says yes, they buy a property there and the matter is dealt with. To expect Caroline to educate her kids there as well was the sort of sexist demand women candidates faced in the 1990s."

Spelman and her husband, Mark, an energy expert, found the requirement burdensome because their lives were centred in London. It is understood that they complied with the demand when their children were young. But they then moved to bigger schools outside Meriden.

The investigation into Spelman's allowances will be embarrassing because she has been overseeing inquiries into alleged wrongdoings by Tory MEPs in Brussels.

But David Davis, the shadow home secretary, told BBC1's The Politics Show: "I would be amazed if there's any substance to this. What she is doing is going to see the commissioner on Monday, straightaway - David [Cameron] has always been very clear on this - any doubt at all has got to be cleared up straightaway and dealt with."